Various methodologies have been developed to automatically determine when a machine-placed telephone call made to a telephone subscriber, such as is done by a telemarketing computer calling system, has been answered. Such determinations must be made within a very short time frame, almost instantaneously, so that a calling system can reduce productivity losses and, by connecting a waiting operator to the subscriber without any perceivable delay, increase performance quality.
The more preferable methodologies are based on techniques which detect the voice of an answering subscriber. However, many of the telephone line monitoring sub-systems of present calling systems that implement such techniques cannot detect voice in a sufficiently fast manner. An example of a monitoring sub-system which requires relatively long sampling periods of the input signal is described in U.S. Pat. No. 4,356,348. More advanced techniques, and monitoring sub-systems, have been developed recently which can detect the voice of an answering subscriber almost instantaneously and in a reliable and inexpensive manner. Such a telephone line monitoring sub-system is described in U.S. Pat. No. 4,742,537.
With the growing use of automatic answering machines by subscribers, it also has now become desirable to have a calling system which can determine when a call has been answered by a subscriber or by an answering machine. Upon a determination that a call has been answered by an answering machine, such a calling system could then undertake an alternative action, for example, not connect a waiting operator to the telephone line. If not required to complete the call, the calling system operator can then use the saved time to handle other answered calls that are received by the calling system during a telephone calling campaign.
Ironically, although many present calling systems are slow in detecting and responding to human voice, they are fast enough in detecting and responding to answering machines. For instance, such systems may take advantage of their slow voice detection and further wait to detect whether a voice continues speaking without a long break (such as would normally occur after a subscriber answers a call by saying "hello"), thus indicating a prerecorded message from an answering machine. Clearly, imitation of such a methodology by a system which provides instantaneous voice detection would eliminate the advantage such a system holds with respect to detecting and responding to subscribers. In fact, the loss of productivity of a few seconds in the handling of each call by an "instantaneous voice detection" calling system using such a methodology becomes a net loss for an entire telephone calling campaign by the calling system, even with improved detection and response to answering machines. In addition, the natural start of conversations provided by "instantaneous voice detection" calling systems would be lost. Consequently, there is a need to develop a system and methodology that will detect and respond to answering machines in an efficient, reliable and inexpensive manner while conserving the advantage of an "instantaneous voice detection" calling system.